How to Automatically add a Hyphen to number in a text field

<script language="javascript">
function addhyphen()
{
      str = form1.textfield.value;
      str = str.substring(0,4) + "-" + str.substring(4,str.length);
      form1.textfield.value = str;
}
</script>
<form name = "form1">
<input type="text" name="textfield" onChange="addhyphen();">
</form>

gees, just went away for a while and now i am second in the thread.... :p

Can't get either one to work... I thought the second was a little easier..
This is what I got

function addHyphen() {
    str = foc-helpfeedback.AccountNo.value;
     str = str.substring(0,4) + "-" + str.substring(4,str.length);
     form1.AccountNo.value = str;
     }

<input type="text" name="AccountNo" size="10" onChange="addHyphen()" ; maxlength="11" tabindex="1" tabindex="1" />

What did I miss?

First of all, the second one does the exact same thing as the first one.
Second of all, if "foc-helpfeedback" is the name of a form, I suggest you change it.  Hyphens aren't really good practice in naming elements.

Third of all, change your code to this:

function addHyphen() {
    var str = document.forms['foc-helpfeedback'].elements['AccountNo'].value;
    str = str.substring(0,4) + "-" + str.substring(4,str.length);
    document.forms['foc-helpfeedback'].elements['AccountNo'].value = str;
}

However, this will append a hyphen even if the value is blank.

Additionally, the code I provided worked as-is.  Can't seem to figure out how you couldn't get it to work.

Hmm, strange that mine didnt work for you, i tested mine.
Anyway, I changed it abit, it checks if it already has a hyphen it won't insert the hyphen again

******************************************

<script language="javascript">
function addhyphen()
{
           str = form1.AccountNo.value;
      
      if (str.substring(4,5) != "-")
      {    
            str = str.substring(0,4) + "-" + str.substring(4,str.length);
      }
           form1.AccountNo.value = str;
}
</script>
<form name = "form1">
<input type="text" name="AccountNo" size="20" maxlength="11" tabindex="1" tabindex="1" />
<input name = "button" type ="button" value = "add hyphen"  onclick="addhyphen();">

</form>

Still can't get it to work... I'll look around the web for an answer.

Not sure why you accepted my answer then...

:-/

If you provide your html we'll be able to get you a solution.

Also not sure why you gave a grade of "c".  Both solutions provided to you are functional when used as-is.  You did not provide enough data for a meaningful answer.

speachless :|